Conditions are becoming dry in most ginseng fields, and it may be necessary for growers to begin irrigating once again. This is especially important for those portions of gardens intended for seed production. Moisture stress can also increase plant susceptibility to Alternaria. However, overhead irrigation should be timed to prevent extending the leaf wetness period as much as possible. If possible, irrigate early in the morning when the leaves are already wet from dew.
European chafer adults, which are white grubs in their larval form, are flying now in Norfolk County and mating. Not much is known about the grub life cycle in ginseng. Adult chafers swarm around shrubs and trees beginning at dusk to mate and are large beetles about the size of a June beetle or slightly smaller.
European chafers typically damage ginseng in the seedling year, which means that they would have to lay their eggs the previous summer when the gardens are being prepared for seeding. European chafers lay their eggs in moist soil, usually in grassy areas between late June and early August. Since new ginseng gardens have not been established yet, it is difficult to determine when the adults would have to lay their eggs for the grubs to survive to the seedling year. It is possible that the adults lay their eggs into bare soil in newly erected gardens, particularly in fields with high weed pressure at that time.
Basically, it is important to realize that we know little about the factors that contribute to grub damage in ginseng. If adult chafers are observed flying around posts in a newly erected garden, then consider applying Admire at seeding. Admire is only registered for one application in the life of a ginseng garden at seeding before mulch is laid down. Additional applications are not necessary, are unlikely to result in increased grub control, and contribute towards resistance developing in European chafers. Growers should track grub damage in seedling gardens, go through their field records, and examine the timing of seeding in gardens with grub issues. It may be possible to avoid grubs by altering production practices but more research is required. If you think you have a grub problem in ginseng, we would like to come out and examine the field. Please contact Sean Westerveld or Melanie Filotas at the Simcoe OMAFRA office. Over time we may be able to develop cultural control strategies.